Method for forming a coated paperboard container

ABSTRACT

A method for forming a deep drawn paperboard container coated with a layer of grease and water impermeable polymeric material. A paperboard blank is disposed between and acted upon by a heated mandrel and a heated mold to form a container. The surface of the blank engageable by the mandrel bears the polymeric coating, and means are operative relatively to move the mandrel and mold toward one another, to engage, the blank, and, just prior to fully engaging the blank to set the same, to introduce a film of air between the heated mandrel and the polymer coated surface to ensure against sticking of the coating to the mandrel.

This is a continuation, of application Ser. No. 208,624, filed Nov. 20,1980 now abandoned, which is a continuation of Ser. No. 065,581, filedAug. 10, 1979, now abandoned which is a division of Ser. No. 968,014filed Dec. 11, 1978 and now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to containers, and more particularly to improvedmethod for forming deep drawn containers from paperboard. While ofbroader applicability, the invention is directed to improvements informing paperboard containers having liquid impermeable surfacecoatings.

In the molding of containers from paperboard blanks coated with liquidimpermeable materials such as, for example, polymeric materials, effortsat preventing sticking of such coatings to heated elements of the moldstructure have involved use of release agents, such as, for example,silicone. Materials of this type, however, add to the cost of the rawmaterials, and, in amounts required to be effective, are not compatiblewith food and drug laws. Also, coatings of polytetrafluoroethylene,available under the trademark "Teflon", have been applied to thesurfaces of the mold structure to prevent sticking, but tend to breakdown and become ineffective after short periods of usage.

U.S. Pat. No. 4,026,458, believed material to the examination of thisapplication, teaches deep drawing a polymer coated paperboard containerof the hereinabove mentioned type from a coated paperboard blank. Theblank is disposed between heated mandrel and mold elements, and theseelements are moved toward one another to form and set the container.Application of heat ensures setting of the paperboard blank so that itwill not revert to its flattened mode. To avoid sticking of the heatedmandrel to the coating, the temperature of the mandrel is maintained ata lower, non-sticking temperature than the temperature of the mold. Forexample, the mandrel is maintained below about 195° F. while the mold ismaintained at between 200° F. to 350° F. It has been found, however,that this lower temperature of the mandrel does not always ensureadequate setting of the paperbord fibers to achieve dimensionalstability in the finished container.

It is a general objective of this invention to provide improved methodfor forming a coated paperboard container that consistently achievesfull setting of the fibers without damage to the coating.

SUMMARY OF THE INVENTION

In achievement of the foregoing as well as other objectives andadvantages, the invention contemplates improved method for forming adrawn paperboard container having at least one side coated with a layerof heat degradable, liquid impermeable material, wherein a paperboardblank coated on at least one side is disposed between and engageable byheated mandrel and mold elements relatively movable toward one anotherto form a container, and introducing a film of compressible fluidbetween one of said mold elements and the recited one side of said blankimmediately prior to fully engaging the blank to set the same, to ensureagainst degradation of the material of said coated layer.

The manner in which the foregoing objectives and advantages of theinvention may best be achieved will be more fully understood from aconsideration of the following description, taken in light of theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective showing, on a reduced scale, of a coatedpaperboard container made according to the invention;

FIG. 2 is a fragmented sectional showing, on an enlarged scale, of thecontainer taken along the line 2--2 in FIG. 1, and looking in thedirection of arrows applied thereto;

FIG. 3 is a top plan view of a coated paperboard blank from which thecontainer seen in FIG. 1 is made.

FIG. 4 is a fragmented sectional view, in elevation, of retractedmandrel and mold structure embodying apparatus aspects of the invention;

FIG. 5 is an enlarged sectional showing of a portion of the apparatusseen in FIG. 4, and illustrating engaged mandrel and mold structure; and

FIG. 6 is a view of a portion of the apparatus shown in FIG. 1, as seenlooking in the direction of arrows 6--6 applied thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With more detailed reference to the drawing, there is seen in FIGS. 1and 2 a drawn container 10 of paperboard sheet 11, made from, forexample, conventional bleached sulphate or sulphite pulps, or mixturesthereof, coated on its inner side with a layer 12 of water and greaseresistant polymeric material, such as, for example polyester. Apolyester found useful comprises polyethylene terephthalate (PET). Othermaterials suitable for coatings comprise polyethylene, polypropylene,polysulfone and polyamide. Preferably, although not necessarily, thepaperboard sheet 11 is from about 18 point caliper to about 24 pointcaliper, and the layer 12 of polyester coating is from about 1 mil toabout 1.5 mils thick. The container is of generally rectangularconfiguration, comprising a bottom wall 13, side and end walls 14 and15, respectively, flaring outwardly therefrom. Walls 14 and 15 arejoined at corners by curved walls 16, and terminate in a peripherpalflange 17.

In FIG. 3 there is seen a coated paperboard blank 10a from whichcontainer 10 is molded. The blank 10a is of substantially rectangularconfiguration with arcuate corners 10b. It is of course to be understoodthat other configurations, such as, for example, square or circular, arecontemplated by the invention. The illustrated side of blank 10a isprovided with the coating layer 12, and the same side is provided at thecorners with spaced, radially extending short score lines 20 and longscore lines 21, disposed in alternate sequence. It is the protection ofcoating layer 12, during molding of the container 10 from blank 10a, towhich the invention is particularly directed. The score lines 20 and 21advantageously are disposed and adapted, and as will be more fullyappreciated from what follows, to accommodate flow of excess paperboardinto the small spaces defined by the score lines in provision ofrelatively smooth pleatings in curved corners 16 and corner portions offlange 17.

With reference to FIG. 4, there is seen an improved apparatus 30 forforming containers 10, and comprising frame structure provided with abed 31 and a plunger 32 mounted on suitable known means (not shown) forreciprocable movements toward and away from bed 31. A mold 33 issupported on bed 31 and a mandrel 34 is supported on plunger 32 forcoaction with mold 33.

Further to the structure of mold 33, a ring 35 mounted on the undersideof the mold clamps an electrical resistance heating element 36 ofgenerally annular configuration in high heat exchange relationship withmold 33. A knockout 37 is provided in mold 33, and comprises a flat,container-engaging member 38 having its face, in extended position,flush with the upper rim 39 of the mold 33. The mold 33 further includesupwardly extending, outwardly divergent side and end walls 40 and 41respectively, terminating in respective downturned, curved rim portions42 and 43. It is to be noted that the contour of the mold as thus fardescribed corresponds substantially to the lower, outer contour ofcontainer 10 as seen in FIG. 1. A pressure ring 58 is disposed aboutmold 33, and is urged into extended position by suitably positionedsprings, one of which is seen at 59.

Further to the construction of mandrel 34, ram 32, and associatedelements, the mandrel includes a central flat rectangular wall 44parallel with the bottom surface of mold 33. Side and end walls 45 and46, respectively, extend upwardly and diverge outwardly from wall 44,and terminate in curved sections, 47 and 48 respectively. A pressurering 49 is disposed about mandrel sections 47, 48, and includes curved,grooved surfaces 50 and 51 that in essence are extensions of curvedsections 47 and 48. Ring 49 is resiliently mounted by springs on mandrel34, one of which is seen at 57, and is movable relative to the mandrelbetween an extended position in which its grooves 50 and 51 clamp theedges of a blank 10a against curved surfaces 47 and 48 upon engagementof the blank by the mandrel, and a retracted position to be described. Apair of electrical resistance heating elements 52 are disposed in highheat exchange relation with mandrel 34.

Further to the construction of mandrel 34, supply conduits 53 and 54 fora compressible fluid, such as air, for example, extend therethrough,and, as seen further to advantage in FIG. 6, terminate in elongate slots55, 56, respectively, that extend generally parallel to the edges of themandrel. Slots 55 and 56 are dimensioned to be restrictive to air flow,permitting sufficient air discharge to produce a film of air between themandrel 34 and the coated side of a blank 10a upon substantially fullengagement of the blank by the mandrel and mold, for reasons to bedescribed in what follows, and in connection with FIG. 5.

Considering now operation of the apparatus in more detail, in aretracted position of mandrel 34, as is illustrated in FIG. 4, pressurering 49 is in its extended position, as respects the mandrel, under theurging of mounting springs 57. Also, pressure ring 58 is in its extendedposition, under the urging of springs 59. While the mandrel is inretracted position, a paperboard blank 10a is placed over mold 33 withits polymer coated side facing the mandrel and portions of its lowersurface resting on knockout plate 37, on rim 39 of the mold, and on aflat surface 58a of lower pressure ring 58. Heating elements 36 and 52are energized, under control of known suitable thermostatic means (notshown), to maintain substantially identical temperatures of the mandreland mold, preferably in the range from about 200° F. to about 350° F.

With blank 10a in place, heated mandrel 34 is moved by plunger 32 towardthe blank and mold 33, whereupon the upper and lower peripheral surfacesof the blank are clamped between a flat surface 49a of ring 49 and flatsurface 58a of ring 58, frictionally to retain the blank in place forengagement by mandrel 34. As plunger 32 continues its downward movement,mandrel 34 engages the central portion of the blank and continuesdownwardly all the while urging it toward conformity with mold 33 andwith retracted knockout plate 38, to its outside, and toward conformitywith mandrel 34, to its inside. Also, pressure ring 49 engages theperiphery of the blank and urges it against the downturned rim 42, 43further to retain the blank and to form peripheral flange 17. Downwardmovement of the mandrel is accommodated by resilient mountings of rings49 and 58 on their respective springs 57 and 59.

As mandrel 34 is moved to within 1/16 inch of full closing while blank10a is engaged, pressurized air from a known, suitably controlled source(not shown) is introduced to conduits 53, 54 for flow through slots 55and 56 to the space between the mandrel and the coated side of theblank. With the aid of the air sealing effect derived from clamping theblank between ring 49 and rim 42, 43, the air is confined in thedescribed space in the form of a film, designated generally by theletter F, adequately to function as a protective thermal barrier orcushion between mandrel 34 and the coating layer 12, while accommodatingtransfer of sufficient heat from mandrel 34 to coact with heat from mold33 to set the shaped container 10 in the fully closed position of themandrel shown in FIG. 5. Presence of the confined film of air preventscoating layer 12 from adhering or sticking to the mandrel surface, andassures a quick release as the mandrel is retracted from closed positionand the container is ejected by plate 38 of knockout 37. To facilitatethe drawing operation, and in accordance with usual practice, the blankengaging surfaces of both mandrel 33 and mold 34 are chromium plated.

From the foregoing, it will be appreciated that the invention affords animproved molding method useful in damage-free formation of containerslined with protective coatings from paperboard blanks bearing suchcoatings.

While preferred embodiments and practices have been described, it is tobe understood that the invention is susceptible of such modifications asmay fail within the scope of the appended claims.

I claim:
 1. A method of deep drawing a container from a paperboard blankhaving a layer of polymeric material on at least one side thereof,comprising the steps of: providing a female mold and a mandrel havingthe shape of the outside and inside, respectively, of said container,and movable between an open position and a blank forming closedposition; disposing said blank between said female mold and said mandrelin said open position thereof, so that said side having said layer ispresented toward said mandrel; heating said female mold and said mandrelto temperatures in a range of from about 200° F. to about 350° F., saidtemperatures being sufficient to set the paperboard blank and capable ofdamaging said layer; relatively moving said heated female mold and saidheated mandrel toward one another into the recited closed positionthereof to engage said blank and urge the latter into conformity withsaid female mold and said mandrel; and, just prior to movement to therecited closed position of said female mold and said mandrel,introducing and confining a film of compressible fluid between saidmandrel and said side of said blank and said layer to ensure againstdamage to the latter by said heated mandrel.
 2. The method of claim 1,wherein said layer of polymeric material is from about 1 mil to about1.5 mils thick, and said paperboard is from about 18 point caliper toabout 24 point caliper.
 3. The method of claim 1 or 2, wherein saidpolymeric material is selected from the group consisting of polyester,polyamide, polypropylene, polyethylene, and polysulfone.
 4. The methodof claim 3, wherein said compressible fluid is introduced as recitedupon relative movement of said female mold and said mandrel to withinabout 1/16 inch of said closed position.
 5. The method of claim 3,wherein said compressible fluid is air.
 6. The method of claim 5,wherein said compressible fluid is introduced as recited upon relativemovement of said female mold and said mandrel to within about 1/16 inchof said closed position.
 7. A method of deep drawing a container from apaperboard blank having a layer of polymeric material on at least oneside thereof, comprising the steps of: providing a female mold and amandrel having the shape of the outside and inside, respectively, ofsaid container, and movable between an open position and a blank formingclosed position; disposing said blank between said female mold and saidmandrel in said open position thereof, so that said side having saidlayer is presented toward said mandrel; heating said female mold andsaid mandrel to substantially the same temperature in a range of fromabout 200° F. to about 350° F., said temperature being sufficient to setthe paperboard blank and capable of damaging said layer; relativelymoving said heated female mold and said heated mandrel toward oneanother into the recited closed position thereof to engage said blankand urge the latter into conformity with said female mold and saidmandrel; and, just prior to movement to the recited closed position ofsaid female mold and said mandrel, introducing and confining a film ofcompressible fluid between said mandrel and said side of said blank andsaid layer to ensure against damage to the latter by said heatedmandrel.
 8. The method of claim 7, wherein said layer of polymericmaterial is from about 1 mil to about 1.5 mils thick, and saidpaperboard is from about 18 point caliper to about 24 point caliper. 9.The method of claim 7 or 8, wherein said polymeric material is selectedfrom the group consisting of polyester, polyamide, polypropylene,polyethylene, and polysulfone.
 10. The method of claim 9, wherein saidcompressible fluid is introduced as recited upon relative movement ofsaid female mold and said mandrel to within about 1/16 inch of saidclosed position.
 11. The method of claim 9, wherein said compressiblefluid is air.
 12. The method of claim 11, wherein said compressiblefluid is introduced as recited upon relative movement of said femalemold and said mandrel to within about 1/16 inch of said closed position.13. A method of deep drawing a paperboard container, comprising:providing a female mold and a mandrel operative for engagement with oneanother in a closed disposition thereof; providing a paperboardcontainer blank having a layer of liquid impermeable material on atleast one side thereof, said material comprising a polymer coatingselected from the group consisting of polyester, polyamide,polypropylene, polyethylene, and polysulfone; disposing said blankbetween said female mold and said mandrel so that said side having saidlayer is presented toward said mandrel; heating said female mold andsaid mandrel to substantially the same temperature in a range from about200° F. to about 350° F., said temperature being sufficient to set thepaperboard blank; relatively moving said female mold and said mandreltoward one another into the recited closed disposition thereof to engagesaid blank and urge the latter into conformity with said female mold andsaid mandrel; and, just prior to movement to the recited closeddisposition of said female mold and said mandrel, introducing andconfining a film of compressible fluid between said mandrel and saidside of said blank having said layer.
 14. The method of claim 13,wherein said polymer coating is from about 1 mil to about 1.5 milsthick, and said paperboard is from about 18 point caliper to about 24point caliper.
 15. The method of claim 13 or 14, wherein saidcompressible fluid is introduced as recited upon relative movement ofsaid female mold and said mandrel to within 1/16 inch of said closeddisposition thereof.
 16. The method of claim 13 or 14, wherein saidcompressible fluid is air.
 17. The method of claim 16, wherein saidcompressible fluid is introduced as recited upon relative movement ofsaid female mold and said mandrel to within 1/16 inch of said closeddisposition thereof.
 18. The method of claim 1, 7 or 13, wherein saidblank is placed over said female mold, and said mandrel alone is movedfrom the recited open position toward said female mold into the recitedblank forming closed position of said female mold and said mandrel. 19.The method of claim 18, wherein said compressible fluid is introduced asrecited upon movement of said mandrel to within about 1/16 inch ofclosed position with said female mold.